Variable capacitive diodes (also referred to as, for example, varactor (Variable Reactor) diodes or varicap (Variable Capacitor)) are often used for switching of a radiation pattern of an antenna (radiation directivities, or simply, directivities) or its operation frequency (the frequency at which the antenna works). As such an antenna, for example, an antenna is known that includes a non-excitation element (also referred to as a passive element or a parasitic element) in the vicinity of a driven element (which is directly connected with a feeder path) to control the directivities by changing the value of the reverse bias applied to the variable capacitive diode loaded on the non-excitation element.
A technique is also known in which a variable capacitive diode is used for a matching circuit of a monopole antenna on a ground plate and the value of the reverse bias applied to the variable capacitive diode is changed to change the matching frequency between the antenna and the feeder path, namely, to change the operation frequency of the antenna (see Patent Literature 1, for example).